The commander of a police officer killed when her patrol car was struck by a stolen 4x4 said he and fellow officers were devastated at the loss of a colleague they all loved.

Pc Philippa Reynolds, 27, from the Greater Belfast area, died when the unmarked car she was travelling in turned into the path of the speeding jeep, which had just run a red light, in Londonderry around 3.40am.

Two men have been arrested by officers investigating the fatal incident on the Limavady Road.

Ms Reynolds, a former teacher, had been in the Police Service of Northern Ireland (PSNI) for two years.

"She was enthusiastic, bubbly and had a beautiful personality," he said.

"She was just loved by her colleagues and she turned that love to the community she served."

The patrol car was turning a corner when the stolen silver Toyota Land Cruiser hit it side on.

Mr Cargin said he believed the officer, who was sitting in the rear driver's side seat, would have died instantly due to the force of the impact.

Two other officers in the car sustained non-serious injuries.

The commander said it could have been any vehicle turning the corner into the path of the 4x4.

"It could have been anyone, it could have been a family that was struck," he said.

He said the policewoman was one of the most enthusiastic he had worked with.

"She was a young 27-year-old officer, just two years service, in the prime of her life, doing what she loved to do - and that was serving the community to the best of her ability," he said.

"Her colleagues are devastated, as I am as her commander, as we all are as a police service."

Police had been hunting for two males that had made off from the scene in the direction of the Ebrington area.

The arrested men are aged 23 and 25. They are currently being questioned in police custody.

The Toyota was stolen in the Gobnascale area of Derry around 3am.

Mr Cargin appealed to anyone who had seen the vehicle from that time, or who witnessed the crash, to come forward.

Northern Ireland's chief constable has vowed to bring to justice those responsible.

Matt Baggott said he was greatly saddened by the death of his colleague.

"This is a personal tragedy for her family and also for the whole Police Service," he said.

"She was out on duty, working to keep people safe, when she died. My thoughts and prayers are with her family at this time.

"I and my colleagues will ensure that no stone remains unturned as we work to bring to justice those who perpetrated this crime".

Northern Ireland Secretary Theresa Villiers said: "This is a tragic waste of a young life in sad and reckless circumstances. Constable Reynolds died as she went about her job keeping people safe in the community she served.

"I send my sincerest condolences to her bereaved family and colleagues. And I wish the two injured officers a full and quick recovery.

"I urgently appeal to anyone with information to assist the PSNI in bringing the people responsible for Constable Reynolds' death before the courts."

Stormont Justice Minister David Ford said his thoughts were with the policewoman's relatives and the injured officers.

"I was shocked to hear of this tragic incident which resulted in the death of a police constable who was carrying out her duties serving the community in the middle of the night," he said.

"My thoughts and prayers are with her family at this time.

"I also send my best wishes to the two officers injured in this incident for a speedy and full recovery. It is hard to imagine how they, and indeed the wider PSNI family, are feeling.

"This is not the first time we have seen death and injury resulting from car crime. I call on those engaged in this crime to reflect on the consequences of their actions and stop this senseless activity."

The Northern Ireland Police Ombudsman's office has been informed.

Police have appealed for witnesses to come forward.

The Limavady Road at its junction with Glendermott Road and Clooney Terrace has been closed while investigations are carried out.

Chair of the Northern Ireland Policing Board Brian Rea also expressed his sympathies.

"On behalf of the Policing Board I would like to offer deepest condolences to the family, friends and colleagues of this young women," he said.

"They will have received the terrible news this morning and will be devastated by this tragic event.

"Our thoughts are also with the two police officers in the car at the time of the collision, who managed to escape without serious injuries.

"To lose a colleague, out on patrol protecting the community, is a terrible blow to the PSNI and I would appeal to anyone who has any information about this incident to go to the police immediately."

The most senior police officer in the Republic of Ireland, Garda Commissioner Martin Callinan extended his condolences.

"Our thoughts and sympathies are with our friends in Northern Ireland as they mourn the loss of their colleague," he said.

"We also wish a speedy recovery to the officers injured in the incident."